'Virtual Colonoscopy' Boosts Colon Cancer Screening Rates

by John Gever John Gever,Senior Editor, MedPage Today
November 14, 2011

Action Points

Explain that when offered CT colonography, also known as virtual colonoscopy, substantially more people in a large study underwent screening than when conventional colonoscopy was the only option.

Point out that the current study suggested that CT colonography may be less sensitive for finding advanced neoplasia.

When offered CT colonography, also known as virtual colonoscopy, substantially more people in a large study underwent screening than when conventional colonoscopy was the only option, Dutch researchers said.

In a randomized, population-based trial, 34% of people offered CT colonography were screened, compared with 22% of those offered standard colonoscopy (P<0.0001), reported Evelien Dekker, MD, of Academic Medical Center in Amsterdam, and colleagues.

A total of 5,924 people in the Amsterdam and Rotterdam areas, ages 50 to 75, were invited for primary screening for colorectal cancer and 2,920 were offered CT colonography without cathartic bowel preparation. The different response rates worked out to a relative risk for screening of 1.56 (95% CI 1.46 to 1.68) favoring the CT-based procedure. Dekker and colleagues reported online in Lancet Oncology.

The results help fill a major gap in knowledge about CT colonography -- whether its attractions relative to conventional colonoscopy will induce more patients to be screened.

It has been speculated that CT colonography would be more popular because it's noninvasive, as well as faster, and therefore has less of an "ick" factor for patients than colonoscopy. Complication rates are also lower because the mechanical colonoscopy probe can injure the bowel wall.

Skeptics, however, have pointed out that the hypothesis had not been tested directly and argued that there was reason to doubt it.

Any suspicious findings from CT colonography must be followed up with a standard colonoscopy, meaning that patients must return for a second procedure. In addition, the CT scan carries a small risk of radiation-induced cancer.

Finally, doubts have been raised as to its efficacy. Some studies have found that CT colonography is less sensitive for detecting precancerous polyps, although others have indicated that so-called yield rates are similar with the two procedures.

CMS cited these arguments in 2009 when it declared that Medicare would not cover CT colonography.

The current study suggested that, in fact, CT colonography may be less sensitive. The relative risk for finding advanced neoplasia among those undergoing the screening was significantly higher in the colonoscopy group (RR 1.46, 95% CI 1.06 to 2.03).

Complications were nearly nonexistent with both procedures: three bleeding events were seen after CT colonography and two occurred in the colonoscopy group.

But the higher participation rate for CT colonography meant that yields per invitee were nearly equal (1.9 per 100 for CT colonography versus 2.1 per 100 for colonoscopy, P=0.56).

On the basis of the latter finding, Dekker and colleagues concluded that "both techniques can be used for population-based screening for colorectal cancer."

"Other factors such as cost-effectiveness and perceived burden should be taken into account when deciding which technique is preferable," they added.

In an accompanying editorial, Perry Pickhardt, MD, of the University of Wisconsin in Madison, wrote that the study's demonstration of greater participation with CT colonography "is a crucial finding, since this modality could operate in parallel with existing colonoscopic screening."

He suggested that lack of participation in colonoscopy-based screening is the major current problem.

"The bottom line is quite simple -- too many people are dying of a readily preventable disease," Pickhardt wrote. "The issue with screening for colorectal cancer is not related to test efficacy per se, but rather to the willingness of patient participation."

Making CT colonography more widely available as a screening option will increase the overall number of advanced neoplasias discovered and removed, he argued. "The additive yields of having both colonoscopy and CT colonography available as primary screening options could have a profound effect on the incidence and mortality of colorectal cancer in the future."

The study was funded by the Netherlands Organisation for Health Research and Development, Centre for Translational Molecular Medicine, and the Nuts Ohra Foundation.

All study authors declared they had no relevant financial interests. Pickhardt reported serving as a consultant for Medicsight, Viatronix, and Bracco and as cofounder of VirtuoCTC.